The use of protective facemasks has become standard for many health care and other related activities. The primary objective of the facemasks is to filter harmful materials from the inhaled and exhaled air. However, medical facemasks may also be used to protect the wearer from liquid insults. As such, these masks may include an attached clear plastic visor to protect the eyes from liquid splashes. Alternatively, a stand-alone clear face shield may also be worn in conjunction with the filtering mask.
One continuing problem attendant with the use of face shields or protective facemasks with attached visors in both medical and industrial applications is fogging of the visor or shield. The warm, moist air exhaled by the wearer will condense on relatively cool surfaces that are in close proximity to the nose or mouth of the user. Condensate droplets will fog or cloud eye glasses, face masks and other protective shields, along with oculars for scientific equipment, such as endoscopes and microscopes. This fogging or clouding results when a high concentration of moisture vapor contained within the protective mask passes through or around the facemask and condenses on a cooler eyeglass in the proximity of the mask. Various techniques have been proposed to solve the problem of fogging, such as described in U.S. Pat. Nos. 4,635,628; 4,419,993; 3,890,966; and 3,888,246.
Nevertheless, many of these solutions fail to solve the problem of glare. Glare is an undesirable specular reflection of light from a surface upon which the light is incident. For instance, personnel working in clean rooms and medical personnel performing lengthy, complex surgical procedures often report eye strain and eye fatigue from such reflections and glare after wearing a facemask for extended periods of time. Eye fatigue from glare is particularly noticeable when using precision scientific equipment, such as microscopes and endoscopes, while wearing a facemask or other protective equipment to protect and/or shield the wearer's face. Many commercial transparent films (e.g., polyester) used to form transparent visors or shields are coated with a thin finish; however, the impact of the finish on optical properties is negligible.
Various techniques have thus been suggested to reduce both fogging and glare in facemasks. For example, U.S. Pat. No. 5,813,398 to Baird, et al. describes a facemask having a filter body with a layer of fluid impervious film disposed over an upper portion of the facemask to block air exhaled by the wearer through the filter body from fogging eyeglasses and/or an eye piece. A layer of non-woven material is preferably placed over the fluid impervious film layer to substantially reduce and/or eliminate any glare from the fluid impervious film layer. In addition, U.S. Pat. Nos. 5,585,186 to Scholz, et al.; 5,723,175 to Scholz, et al.; 5,753,373 to Scholz. et al.; 5,873,931 to Scholz, et al.; 5,997,621 to Scholz, et al.; and 6,040,053 to Scholz, et al. generally describe coating compositions that rely on a solid particles of porous inorganic metal oxide network to impart anti-reflection properties, and very specific surfactants to impart anti-fogging properties. Unfortunately, such techniques for reducing fogging and glare in facemasks are still not adequate. For example, the use of one coating ingredient for anti-reflection (e.g., porous inorganic metal oxides) and another for anti-fogging (e.g., surfactants) is overly complex and expensive. Other issues with surfactant/solid particle dispersions relate to formulation instability over time, which can negatively affect optical properties of the product.
Currently, there is a need for an improved technique for simultaneously eliminating the deleterious effects of fogging and reducing glare on facemasks.